Sidewall transfer methods have recently been developed in the art of manufacturing semiconductor devices. By a sidewall transfer method, a pattern with a size smaller than a minimum feature size (resolution limit width) in photolithography is formed. A sidewall material is disposed around a core material, and layers of the sidewall material (sidewalls) on side surfaces of the core material are connected to each other at end portions of the core material to form a loop shape. As a result, the sidewalls make a closed loop pattern. If a wiring line pattern is formed using this closed loop pattern, adjacent two wiring lines are electrically short-circuited. In order to avoid this, a process of cutting the closed loop pattern to disconnect the two wiring lines (“loop cut process”) is needed.
Conventionally, the loop cut process has been performed using a loop cut mask pattern formed with a photolithographic technique. The size of the closed loop pattern, however, is smaller than the minimum feature size in photolithography. Therefore, it has been difficult to expose the mask pattern to conform to the closed loop pattern. On the other hand, if a margin is obtained in a portion around the closed loop pattern to enable the exposure of the mask pattern, the area penalty in this portion increases.